A general disk drive apparatus has employed as an information recording medium a CD (compact disk) only for playback, a CD-ROM (read-only memory) and so on in which a music data, an information data processed by a computer and so on are previously recorded. An optical disk such as a write-once type OD (magneto-optical disk) or the like on which data can be recorded again is also employed as the information recording medium.
A disk drive apparatus for storing and/or reproducing information by using these optical disks as an information recording medium has a disk table fitted to a rotation shaft of a spindle motor, an optical pickup device for writing and/or reading an information signal on and/or from an optical disk loaded onto the disk table. The optical disk is horizontally loaded onto the disk table and then rotated while a light beam is irradiated by an objective lens of an optical pickup device on an information recording surface of the optical disk. Then, while He objective lens is moved in parallel to the information recording surface, information is recorded on the information recording surface and information previously recorded thereon is reproduced.
When such disk drive apparatus is used to record and/or reproduce data on and/or from the optical disk with satisfactory recording and reproduction characteristics, the objected lens of the optical pickup device for reading the information on the information recording surface of the optical disk must be positioned and inclined at an angle within a predetermined range relative to the information recording surface of the optical disk. The reason for this is that inclination of the objective lens largely depends upon accuracy of reproduction of the information signal.
In this case, if the optical disk is recorded and/or reproduced with high density and high accuracy, then it is preferable to set an optical axis of the objective lens perpendicularly (90.degree.) to the optical disk. If the light beam is made incident on the information recording surface of the optical disk vertically, then a beam spot of the light beam irradiated on the information recording surface has a circular shape. As a result, it becomes possible for the beam spot to precisely scan one recording track formed on the information recording surface, and hence it is possible to record and/or reproduce data with satisfactory recording and reproduction characteristics.
However, inclination of the optical disk, a vertical-direction posture of a spindle motor, a vertical-direction posture of an objective lens and so are fluctuated, which makes it difficult to accurately set an optical axis of the objective lens perpendicularly to the optical disk. Therefore, in the disk drive apparatus employing an optical disk as an information recording medium, in consideration of inclination of an optical disk, accuracies in attachment of a spindle motor and an optical pickup device and so on, an allowance of a relative inclination of an information recording surface of the optical disk relative to an optical axis of an objective lens is determined in the standard.
An disk drive apparatus using an optical disk, such as a CD, a CD-ROM or the like, having a diameter of 12 cm is standardized to have an allowable range for the relative inclination angle between the optical disk and the objective lens which is determined to be 1.2.degree. or less (the inclination of the optical disk is standardized to be 0.6.degree. or less and the inclination of each of the spindle motor and the objective lens of the disk drive apparatus is standardized to be 0.6.degree. or less). The objective lens is moved with reference to a reference state that the optical disk is attached to a predetermined position, and thereby the optical axis of the objective lens is adjusted so that its inclination should fall within a predetermined inclination range.
Two types of optical disks, such as a CD, a CD-ROM or the like, having a diameter of 12 cm and classified on the basis of the degree of the recording density have been manufactured. One of the two types of the optical disks is a first optical disk, such as a CD, a CD-ROM or the like, having a standard information recording density (hereinafter called as a "standard density disk"), while the other thereof is a second optical disk such as a DVD (a Digital Video Disk), a HD-CD (a High Density Compact Disk) and so on, having a recording density which is seven to eight times as large as that of the CD and the like (hereinafter called as a "high density disk").
In general, while the standard density disks are manufactured with a relatively rough dimension accuracy, the high density optical disks are manufactured with a precise dimension accuracy. In order to increase a recording density of the high density disk, a high density disk has not only a narrower width of a recording track where data are recorded but also a narrower pitch between pits in order to set the width and the pitch smaller.
The disk drive employing such high-density optical disk as an information recording medium must set a vertical-direction posture of an object lens relative to the optical disk with higher accuracy, employ more highly accurate parts, set an inclination angle of the optical disk smaller, or further improve an adjustment accuracy. However, these attempts inevitably encounter their limits. For example, the attempt of further improving the adjustment accuracy leads to increase of a manufacturing cost of a product, and hence it is not preferable.
Moreover, if the optical disk is an LD (laser disk), then the LD has a large disk diameter of 300 mm and is formed of AS (acrylonitrile styrene resin) whose rigidity is lower as compared with PC (polycarbonate) used as a disk material for a CD and so on. Accordingly, an inclination amount of the LD becomes larger.
The applicant of the present invention has filed various patent applications relating to such disk drive apparatus having a skew adjustment mechanism for adjusting an optical axis of an objective lens of an optical pickup device relative to a warp of an information recording surface of the optical disk. The skew adjustment mechanism inclines the optical pickup device equipped with the object lens used for reading an information signal in accordance with an inclination of the optical disk or inclines the spindle motor in accordance with the inclination of the optical pickup device.
Such skew adjustment mechanism will be described in detail. The skew adjustment mechanism has a pair of rotation fulcrums formed on a horizontal reference line passing through an axial line of a rotational shaft of the spindle motor and perpendicular to a tray center. The spindle motor is rotated around the pair of the right and left rotation fulcrums, and thereby the inclination of the optical disk relative to the optical axis of the objective lens can be adjusted. Since the above-mentioned skew adjustment mechanism is arranged to perform the radial skew adjustment of the optical disk by adjusting the inclination of the spindle motor, its structure can be simplified and a required drive force can be reduced as compared with that for adjusting the inclination of the overall body of the optical pickup. Therefore, a small-sized, low-cost and power-saving disk drive apparatus can be obtained.
However, the above conventional disk drive apparatus does not accurately set a positional relationship between the optical disk and the optical pickup to a predetermined initial state. The above disk drive apparatus detects whether the optical disk used for recording and/or reproducing information has a high density or a low density. If the optical disk is a high-density disk, the skew adjustment mechanism is operated to perform the skew adjustment, and, if on the other hand the optical disk is a standard-density disk, the skew adjustment mechanism is stopped and the skew adjusting is not carried out. Therefore, the conventional disk drive apparatus encounters the problem of unsatisfactory reproduction upon exchange of the optical disk from a high-density disk to a standard-density disk.
The above-mentioned problem arises due to the following causes. The causes will hereinafter be described with reference to FIG. 35 to FIG. 37. FIG. 35 to FIG. 37 are diagrams used to explain a relationship between an optical pickup and an optical disk of the conventional disk drive apparatus. In FIGS. 35 to 37, reference numeral 290 represents a subchassis, reference numeral 291 represents a spindle motor secured to the sub-chassis 290, and reference numeral 292 represents a disk table attached to the rotational shaft of the spindle motor 291. An optical disk D (a high-density disk Dh or a standard-density disk Ds) is horizontally loaded on the disk table 292 so as to be rotatable integrally therewith.
Moreover, an optical pickup device 293 for writing and/or reading information to and/or from the optical disk D loaded onto the disk table 292 is slidably attached to the subchassis 290. The optical pickup device can be brought close to and away from the disk table 292 in a state where an objective lens 294 thereof is opposed to an information recording surface of the optical disk D. A skew sensor 295 is attached to the optical pickup 293 with facing upward. The skew sensor 295 detects an inclination of the optical disk D.
Thus, as shown in FIG. 35, if the high-density disk Dh is loaded onto the disk table 292 fixed on the rotation shaft of the spindle motor 291, then the information recording surface is inclined in a direction in which the high-density disk becomes closer to the objective lens 294, as shown by a two-dot chain line. At this time, as shown in FIG. 36, while the object lens 294 of the optical pickup device 293 is moved in a direction in which it is brought away from the information recording surface, the skew adjustment mechanism acts to incline the optical axis of the object lens in a direction perpendicular to the information recording surface. When the high-density disk Dh is ejected, as shown in FIG. 37, the object lens 294 is held in a state that it is inclined.
When the standard-density disk Ds is inserted into the disk drive apparatus in the above state and loaded onto the disk table 292, a disk-kind discriminating means discriminates whether the inserted disk has a high density or a low density similarly to the preceding processing. Since the disk loaded at this time is the standard-density disk Ds, then the skew adjustment mechanism is not operated. However, similarly to the high-density disk Dh, the an outer periphery side of the loaded standard-density disk Ds is inclined downward due to a weight of the disk.
However, since the standard-density disk Ds has a recording pitch, a rotation speed, a physical disk structure and so on which are different from those of the high-density disk Dh, the inclination angles of the information recording surfaces of the standard-density disk and the high-density disk relative to the optical axis of the light beam are different from each other.
Accordingly, if the standard-density disk is inserted in a state that the inclination of the objected lens 294 has already been adjusted so as to correspond to the high-density disk Dh, then a harmful influence may occur. Specifically, the light beam irradiated from the objective lens 294 is prevented from being focused on the information recording surface, and hence a positional relationship between the standard-disk Ds and the objective lens 294 is prevented from being set in the most satisfactory state for reproducing information recorded on the standard-density disk Ds.
The present invention is made in view of such problems. It is an object of the present invention to provide a disk drive apparatus which, when an optical disk is newly loaded thereto to record and/or reproduce information thereon and/or therefrom, returns a positional relationship between the optical disk and an optical pickup device to it predetermined initial state and then operates a skew adjustment mechanism if necessity is caused, thereby making it possible to selectively employ plural kinds of optical disks having different specifications such as recording capacities or the like.